Molybdenum: the essentials

Molybdenum is a silvery-white, hard, transition metal. Scheele discovered it in 1778. It was often confused with graphite and lead ore. Molybdenum is used in alloys, electrodes and catalysts. The World War 2 German artillery piece called "Big Bertha" contains molybdenum as an essential component of its steel.

Molybdenum: historical information

Molybdenum was discovered by Carl William Scheele in 1781 at Sweden. Origin of name: from the Greek word "molybdos" meaning "lead".

In 1778 Carl Welhelm Scheele conducted research on an ore now known as molybdenite. He concluded that it did not contain lead as was suspected at the time and reported that the mineral contained a new element that he called molybdenum after the mineral. Molybdenum metal was prepared in an impure form in 1782 by Peter Jacob Hjelm.

Molybdenum is a necessary element, apparently for all species. Only very small amounts are required. Molybdenum plays a role in nitrogen fixation, (a process by which the normally unreactive nitrogen gas is turned into other compounds) enzymes, and nitrate reduction enzymes.

Molybdenum is not found as the free metal. The main ore is molybdenite (molybdenum sulphide, MoS2). Molybdenum is recovered as a by-product of copper and tungsten production.

Isolation

Isolation: it is not normally necessary to make samples of molybdenum metal in the laboratory since it is readily available commercially. Industrially, its extraction is sometimes linked to copper production. The normal process is for the sulphide MoS2 to be "roasted" to form the oxide MoO3. This is often used directly in the steel industry.

Pure samples of the metal are available by first dissolving the oxide in ammonium hydroxide to make ammonium molybdate, (NH4)2[MO4], and thenreduction of the molybdate with hydrogen gas to form the metal.

The Molybdenum isotope Mo-95 is used for the production of the medical radioisotope Ru-97. Mo-96 is used for the production of the radioisotopes Tc-96 and Tc-95m, both of which have a medical application. Most Mo isotopes are also used in nutrition studies in humans. Depleted Mo-95 has been suggested for use in UMo fuel elements for materials test (high flux) reactors.